1. Field of the Invention
The invention relates to a process for extracting aqueous ketazine solutions, in particular for isolating ketazine from aqueous solutions resulting from the preparation of hydrazine.
2. Brief Description of the Prior Art
Hydrazine is prepared according to the xe2x80x9cRaschig processxe2x80x9d by oxidizing ammonia with sodium hypochlorite. Chloramine is formed as an intermediate and reacts further with excess ammonia to form hydrazine. In one variant of the Raschig process, the xe2x80x9cketone processxe2x80x9d, ketones are added to the reaction mixture, and ketazines and possibly hydrazines are formed. Acid hydrolysis of the ketazines can convert these to hydrazine and the corresponding ketone. While the syntheses mentioned above can be carried out in good yields, using simple technical means, the workup of the synthesis solutions, i.e. the removal of the hydrazine, hydrazone and ketazine reaction products, is problematic owing to their low concentration and the high content of inorganic salts and organic reaction partners.
When removing ketazines, a distinction needs to be drawn between processes which can be applied to the removal of dimethylketazine (acetone(1-methylethylidene)hydrazone), which results from the use of acetone in the ketone process, and those processes which are suitable for the removal of higher ketazines which are based on ketone having more than 3 carbon atoms.
DE 1 273 503 B discloses that aqueous solutions of dimethylketazine can be worked up to give ketazine with the aid of dimethylketazine-water azeotropic distillation after preceding expulsion of ammonia. The dimethylketazine is subjected to hydrolysis during the azeotropic distillation, so that operation has to be effected under rapid acetone reflux and in the presence of excess acetone. Owing to its high specific energy demand, this process is costly.
Higher ketazines can likewise be removed from aqueous solutions as a result of minimum azeotrope formation using water. Such a process is described, for example, in DE 1 282 617 B. The removal of higher ketazines by means of adding hydrophilic substances, in particular by adding salts, is also possible. This separates the system into two phases, and the aqueous phase can be removed from the phase containing the ketazines. Such a process is described, for example, in DE 2 056 357 B. A disadvantage of the higher ketazines which can be removed relatively easily is that ketones have to be used which cost more than acetone. In addition, the technical and energy demands of the subsequent hydrolysis to give hydrazine and ketone are higher than for dimethylketazine. Workup measures which are effected by the addition of salts increase the resulting salt burden in an undesirable manner.
GB 1 191 630 B discloses an extractive workup of aqueous ketazine solutions. This document describes the preparation of hydrazine from aqueous ketazine- and hydrazone-containing solutions which is based on extractive hydrazone disproportionation. The extractants used are chlorinated hydrocarbons, aromatic solvents such as benzene and toluene and also alcohols, in order to remove the ketazine forming in addition to hydrazine during the disproportionation of hydrazone from the equilibrium. A disadvantage of this process is that the yields of free hydrazine are only about 60%.
DE 24 36 335 A describes a process for working up aqueous synthesis solutions during hydrazine preparation which involves extracting the synthesis solutions to remove ketazine using organic solvents which are water-immiscible or only slightly miscible. The solvents used were higher alcohols, chlorinated hydrocarbons and also optionally substituted aromatics. The document further describes the dependence of the number of extraction stages to attain a maximum hydrazine yield upon various factors such as salt content, ammonia concentration, concentrations of hydrazine, hydrazone and ketazine, temperature, pressure and molar ratio of ketazine to total hydrazine.
A disadvantage of the process mentioned is that the extract obtained, depending on the extractant used, has a relatively high content of water, acetone and salts. The high water content complicates the isolation of the ketazine, while the high acetone content in the extract results in a multistage extraction achieving a reduced molar ratio of ketone to overall hydrazine in the aqueous phase and leads to deterioration in the partition coefficients. A high salt content has to be reduced by subsequent washing, since it otherwise disrupts the distillative workup. A further disadvantage is that the extraction performance of the extractant diminishes in the course of time which leads to undesirable product losses.
There is accordingly a need for a process for extracting ketazines, preferably from synthesis solutions as result from hydrazine preparation, which does not have the abovementioned disadvantages.
Surprisingly, a process has now been found for extracting aqueous ketazine solutions which is carried out using an aqueous ketazine solution having a salt content of 5 to 27% by weight and an ammonia content of 0 to 28% by weight to extract at temperatures of 50 to 120xc2x0 C., which is characterized in that the ketazine solution to be extracted has a molar excess of 50 to 200% of ketone based on the ketazine to be extracted, and that an aliphatic hydrocarbon extractant is used which has a boiling point of 150 to 300xc2x0 C. at atmospheric pressure.
The process according to the invention facilitates in particular the workup of ketazine-containing synthesis solutions as are obtained from hydrazine preparation. Synthesis solutions from hydrazine preparation are reaction mixtures as are obtained from the known processes after the stage of synthesizing hydrazine, hydrazones and ketazines for the purposes of preparing hydrazines or hydrazine derivatives by oxidizing ammonia, which may also be present in the bound form, using an active halogen or peroxy (xe2x80x94Oxe2x80x94Oxe2x80x94) compound of any type in the presence of further components. Depending on the type of hydrazine preparation, the composition of the synthesis solution may vary. Apart from hydrazine, reaction products of hydrazine with ketones, for example hydrazones, ketazines and water, the following further substances may be present: ammonia, ketones, salt-like compounds, salts and organic components which are necessary for the purposes of the reaction or result from the synthesis, for example nitriles, esters, imides or amides, as are obtained from the known processes which use hydrogen peroxide. Hereinbelow, the molar sum total of hydrazine, hydrazone and ketazine is referred to as total hydrazine. The process according to the invention facilitates the isolation of ketazines and any hydrazones in the form of pure aqueous solutions which can be converted to hydrazine or salts thereof or to other derivatives of hydrazine.